The external fund manager backed by Berkshire Hathaway’s Charlie Munger, Li Lu, makes no bones about it when he says ‘The biggest investment risk is not the volatility of prices, but whether you will suffer a permanent loss of capital.’ It’s only natural to consider a company’s balance sheet when you examine how risky it is, since debt is often involved when a business collapses. We can see that Ardagh Metal Packaging S.A. (NYSE:AMBP) does use debt in its business. But the more important…